The Eisbach River flows through the heart of the English Garden, a 900-acre park -- larger than New York City’s Central Park -- in downtown Munich, Germany. At the south end of the park, near the Haus der Kunst art museum, a one-meter-high man-made wave draws experienced surfers from all over the world.

Known as the Eisbach Wave, it is perhaps the world’s most famous river wave. Surfing has been officially permitted in this spot since 2010, though surfers have been visiting since 1972. (The Eisbach surfing community is profiled in the 2009 movie “Keep Surfing.”)

This past July, my family licked ice-cream cones as we watched this phenomenon of surfers in full wetsuits in the heart of a major city. Lined up 10 deep on either bank of the river, surfers of all ages waited their turn to leap into the Eisbach Wave. Fans and tourists crowded the banks, trying to get a good view.

The surfers were engaging in an activity for mind, body and spirit. Risking their necks for what is known as a difficult and treacherous wave, they were simultaneously reading the water, attending to balance, planning their moves, focusing on their bodies, maintaining awareness of the dangerous concrete weirs, and sometimes playing the crowd.

They were completely in the moment.

A young surfer friend told us that when you surf, you can’t always control what happens. Surfing is about the wave, your body and the energy of the moment. It’s about complete relaxation and complete focus. It’s about accepting that when you fall, it’s done. There is no redo. It’s the next person’s turn.

To make things even more interesting, the day we watched the Eisbach surfers happened to coincide with the World Slackline Masters event in Munich. The city was full of slackliners, there to watch the top four teams -- Japan, Brazil, Switzerland and the U.S. -- compete.

Slacklining involves walking and doing flips and other daredevil maneuvers on a two-inch-wide length of webbing that looks like a tightrope but stretches and bounces like a trampoline.

When the Masters competition was over, one enterprising slackliner from the U.S. team decided it would be a good idea to come to the English Garden and stretch his slackline across the Eisbach Wave, over the heads of the surfers. After securing the line between two trees, he flipped up onto it and started inching his way toward the center of the roiling river.

Our mouths dropped open as he rose and began to walk, ignoring the crashing wave and the surfer who was only a few feet below him. (As we later discovered, he was not the first to attempt this feat.)

Surfing, our friend tells us, is a self-centered endeavor. It is also territorial. You certainly don’t want a crazy slackliner to distract you or fall off his or her line and onto your head.

As we watched, we noticed that both the surfers and the slackliner had to intensify their concentration. One by one, the surfers would move from side to side across the wave, sometimes executing 360-degree turns or flips. The slackliner would bounce up and down, sometimes flipping or somersaulting in the air, landing again on the line. At several points, a surfer would be rising on the wave just as the slackliner was bouncing down, resulting in a near miss.

The actors had to be aware of each other yet completely present in their respective moments. I don’t know whether they improvised around one another or just prayed that they wouldn’t collide. Did they consciously share the space? Were the surfers annoyed that the slackliner had arrived to complicate their activity and take away some fan attention? Did the athletes spontaneously teach one another something about their respective arts? Did they aid one another by sharpening each other’s attention? Were they breaking boundaries into new territory by simultaneously practicing their arts?

As onlookers, we were alternately terrified, impressed, horrified and inspired.

Yes, the slackliner eventually lost his balance and crashed down into the churning wave, narrowly missing a surfer. And yet the gift these athletes gave to us for a few perilous moments was the gift of embodying a complex system of relationships.

They helped us visualize the danger of silos in our work. They helped us see the spirit of adventure required to focus on our work and yet make room for the other -- a task at times harrowing, exciting, exasperating and life-giving.